Many photovoltaic devices, such as solar cells, have multiple junctions of semiconductor materials connected in series to produce electric current in response to receiving different wavelengths of light. Such photovoltaic devices are called multijunction photovoltaic devices (MPDs).
The use of multiple junctions can provide more efficient photovoltaic devices, but characterizing each junction's performance; e.g., determining an amount of current produced by each junction gives rise to additional challenges. One example method for characterizing performance multijunction photovoltaic devices is quantum efficiency (QE) spectroscopy. Quantum efficiency spectroscopy allows determination of a current for each junction of a multijunction photovoltaic device.